These processed Landsat satellite images provide high-resolution
multispectral coverage of selected areas. The characteristics of
the MSS and TM bands were selected to maximize their capabilities
for detecting and monitoring different types of Earth resources.
For example, TM band 2 can detect green reflectance from healthy
vegetation, and band 3 of TM is designed for detecting
chlorophyll absorption in vegetation. TM band 4 is ideal for
near-IR reflectance peaks in healthy green vegetation and for
detecting water- land interfaces. Wavelength of TM band 1 can
penetrate water for bathymetric mapping along coastal areas and
is useful for soil-vegetation differentiation and for
distinguishing forest types. The two mid-IR red bands on TM
(bands 5 and 7) are useful for vegetation and soil moisture
studies, and discriminating between rock and mineral types. The
thermal-IR band on TM (band 6) is designed to assist in thermal
mapping, and for soil moisture and vegetation studies. TM Bands
7, 4, and 2 have been combined to make false-color composite
images. This band combination makes vegetation appear as shades
of red, brighter reds indicating more vigorously growing
vegetation. Soils with no or sparse vegetation will range from
white (sands) to greens or browns depending on moisture and
organic matter content. Water bodies will appear blue. Deep,
clear water will be dark blue to black in color, while sediment-
laden or shallow waters will appear lighter in color. Urban areas
will appear blue-gray in color. Clouds and snow will be bright
white. They are usually distinguishable from each other by the
shadows associated with the clouds. Exposed bedrock will appear
in a wide range of colors depending on the composition and other
factors.

http://pubs.usgs.gov/of/2000/of00-309/OF00-309.DOC